This invention generally relates to a hydraulic brake apparatus for a vehicle. More particularly, this invention pertains to a vehicle hydraulic brake apparatus for regulating a hydraulic pressure outputted from a hydraulic pressure generating source in response to a brake operating force and for supplying a brake hydraulic pressure to first and second wheel brake cylinders via first and second master cylinders in response to the regulated hydraulic pressure.
There have been various vehicle hydraulic brake apparatuses known. As one of the examples of the vehicle hydraulic brake apparatuses, a Japanese Laid-Open Patent Application No. 59(1984)-84652 discloses a hydraulic type brake generating apparatus which represents the vehicle hydraulic brake apparatus, in which a hydraulic pressure outputted from a hydraulic pressure generating source is regulated in response to a brake operating force and the regulated hydraulic pressure is outputted as a brake hydraulic pressure to first and second wheel brake cylinders via first and second master cylinders.
The above-disclosed hydraulic type brake generating apparatus is provided with a tandem type master brake cylinder having first and second pistons and an operating rod operated in response to a brake operating force. A first pressure chamber is defined in front of the first piston and a second pressure chamber is defined in front of the second piston. The first and second pressure chambers are connected to a first and second brake circuits, respectively. According to the hydraulic type brake generating apparatus with this structure, a first hydraulic pressure is applied to both the operating rod and the first piston. The hydraulic type brake generating apparatus is further provided with a control valve device arranged in parallel with the tandem type master brake cylinder. The hydraulic type brake generating apparatus is still further provided with displacement detecting means for the operating rod and at least for one of the first and second pistons. A displacement amount of the operating rod or a displacement amount of the piston is observed by an observing device.
According to the above-described hydraulic type brake generating apparatus, the displacement detecting means for detecting the displacement amount of the piston are directly provided for the master cylinder as illustrated in FIG. 1. In this case, the structure of the hydraulic type brake generating apparatus may be complicated and highly costs for being manufactured. Further, a space of the brake generating apparatus may be limited when being mounted on the vehicle.
Alternatively, a pressure sensor for detecting a hydraulic pressure outputted from the master cylinder can be provided in substitution for the displacement detecting means of the pistons. However, two pressure sensors are required to be respectively connected to the first and second brake circuits. Therefore, the manufacturing cost may be increased. Further, another pressure sensor can be employed for detecting the displacement amount of the operating rod. In this case, the hydraulic type brake generating apparatus requires totally three pressure sensors.
Accordingly, the above disclosed hydraulic type brake generating apparatus is still susceptible of certain improvements with respect to detecting a hydraulic pressure condition of the first and second brake circuits with a simple and down-costed structure.
A hydraulic brake apparatus for a vehicle includes a brake operating member, a hydraulic pressure generating source for generating and outputting a predetermined hydraulic pressure regardless of a brake operation applied to the brake operating member, a regulating valve regulating the hydraulic pressure outputted from the hydraulic pressure generating source in response to a brake operating force applied to the brake operating member and for outputting a regulated hydraulic pressure, a first master cylinder, a second master cylinder, a first hydraulic system, and a second hydraulic system. The first master cylinder includes a first master piston operated in response to the hydraulic pressure outputted from the regulating valve and a first pressure chamber outputting a first brake hydraulic pressure. The second master cylinder includes a second master piston operated in response to the brake hydraulic pressure outputted from the first master cylinder and a second pressure chamber outputting a second brake hydraulic pressure. The first hydraulic system supplies the first brake hydraulic pressure outputted from the first pressure chamber to a first wheel brake cylinder. The second hydraulic system supplies the second brake hydraulic pressure outputted from the second pressure chamber to a second wheel brake cylinder. Further, an output diameter of the first master piston differs from an output diameter of the second master piston.
The hydraulic brake apparatus for a vehicle further includes a pressure detecting means connected to the second pressure chamber for detecting the second brake hydraulic pressure outputted from the second pressure chamber, a brake operating amount detecting means for detecting a brake operating amount of the brake operating member, and a judging means for judging a hydraulic pressure condition of the first and second hydraulic systems based upon the brake hydraulic pressure detected by the pressure detecting means relative to the brake operating amount detected by the brake operating amount detecting means.